χ(3) and optical power limiting measurements of Polyaniline and its derivative Poly (o-toluidine) under CW regime

Abstract

We present the synthesis and results on the third-order optical nonlinearity and optical limiting properties of Polyaniline and Poly (o-toluidine) studied in N,N-Dimethyl Formamide solution using a single-beam z-scan technique. Experiments were performed using continuous wave He–Ne laser operating at 633nm wavelength as an excitation source. The samples exhibit absorption and refraction nonlinearities. The negative sign of the nonlinear refractive index n2 indicates that both materials exhibit self-defocusing optical nonlinearity. The nonlinear refractive index n2, the nonlinear absorption coefficient βeff and the third-order optical susceptibility χ(3) were determined and found to be of the order of 10−7cm2/W, 10−2cm/W and 10−7esu respectively. The FTIR and UV–visible characterization spectra confirm the expected molecular structure of the polymers. Multiple diffraction rings were observed when the samples were exposed to laser beam. The appearance of rings is due to the refractive index change and thermal lensing. The polymer samples with different concentrations exhibits strong optical power limiting under continuous wave laser at the experimental wavelength. Reverse saturable absorption is the dominating mechanism for the observed absorption nonlinearities.